The present invention relates in general to aircraft doors and more specifically to both an improved double door sliding joint design and an improved flight deck door.
Flight deck or flight cockpit doors on commercial aircraft are now required to be intruder proof, yet maintain jam resistant safety features to aid egress/access. One of the more significant design events affecting a flight deck door of a commercial aircraft is a severe emergency landing. During this event, the forward nose gear of the aircraft forces the deck structure under the flight deck to deflect permanently upwards, which can jam the flight deck door. Common flight deck doors are designed to accommodate this deflection, which can be about 10.2 centimeters (cm) (4 inches) relative movement between the floor and the bottom of the door. An exemplary door design to accommodate deck deflection divides the door into a two section door assembly, otherwise known as a xe2x80x9cdutchxe2x80x9d door. An aircraft xe2x80x9cdutchxe2x80x9d door normally has a larger upper door section and a smaller lower door section. The upper door section is hinged to a door frame, allowing the lower door section to accommodate flight deck deflection under the flight deck door. The lower door section includes a telescoping portion or breakaway door panels to aid emergency egress/rescue.
In one exemplary commercial dutch door application, the lower door section is about 35.6 cm (14 in) tall. The lower door section is subdivided into a fixed panel mechanically attached to the larger upper door section, and a telescoping deflection zone to accommodate nose gear/flight deck heave. The deflection zone is designed to deflect upwards into the volume of the fixed panel. The deflection zone is vertically supported, but not horizontally rigid. However, with this dutch door design, an intruder might be able to apply a sufficiently strong forward horizontal force (i.e., by kicking or prying) to the lower door section, dislodging the entire lower section, and through the resulting 14 inch envelope gain access to the flight deck area.
Reducing the height of the lower door section of a dutch door to preclude intruder access to the flight deck area results in a trade-off with the envelope required to accommodate the upward deck deflection caused by nose gear heave. A butted, edge-to-edge door design which offers better horizontal stiffness does not allow the lower door section to displace into the upper door section during a deck displacement event. A unitary door design allowing the lower door portion to crumple during a deck displacement event does not eliminate the potential to jam and prevent access to or emergency egress from the flight deck area.
A simple breakaway lower door section sufficient in size to accommodate deck deflection yet precluding intruder access through the resulting opening is undesirable because it could allow an intruder to force open the lower door section and threaten the operation of the aircraft. It is also undesirable to provide horizontal rigidity to a lower door panel by extending the vertical hinge supporting the upper door section to the lower door section. Extending the hinge would horizontally stiffen the lower door section but it would preclude necessary vertical deflection of the lower section. Extending the hinge to the lower door section edge could also result in damage to the entire hinge section from deck heave, further jamming the entire door assembly.
It is therefore desirable to improve the two section door design of commercial aircraft to provide for flight deck deflection and yet provide an even greater degree of protection against intruder access to the flight deck area.
According to a preferred embodiment of the present invention, a two section door assembly is provided for an aircraft flight deck door. An upper door section height is increased from known designs. A lower door section height is decreased from known designs to preclude intruder access into the flight deck space. To provide for flight deck deflection from landing gear heave, the lower door section is attached to the upper door section using an angled, sliding joint design. The angled, sliding joint (hereafter referred to as the sliding joint for simplicity) design of the present invention has two major members. The first member, the sliding joint upper member, is mechanically joined to a lower edge of the upper door section. The second member, or sliding joint lower member, is mechanically joined to a lower door section upward facing edge.
The sliding joint upper member and the sliding joint lower member of the present invention form an angle to a horizontal plane taken through the sliding joint. At least one engagement element is disposed on both the sliding joint upper member and the sliding joint lower member. The engagement elements slidably engage each other at the above noted angle and are fixed in place by at least one frangible pin located on the flight deck side of the door assembly. The angle of the sliding joint permits the lower door section to dislodge from the upper door section in a shearing motion when a sufficient vertical force such as the landing gear heave is applied. The angle of the sliding joint together with at least one frangible pin prevent a horizontal force, such as that from an intruder, from dislodging the lower door panel.
The engagement elements of the sliding joint are provided with tight clearances to both vertically support the weight of the lower door section and horizontally stiffen the connection between the lower door section and the upper door section. The angle of the sliding joint resists displacement of the lower door section when a horizontal force is applied from the aft or passenger side of the flight deck door. At least one frangible pin provides a positive feature to lock the lower door section in place against a horizontal displacement. The frangible pin(s) is designed to fracture from the vertical load of the deck displacement, however, the frangible pins will not fracture within the range of horizontal forces a human can apply from the passenger compartment side of the door assembly.
In one aspect of the present invention, the frangible pins are provided as shear pins which have an attached pin retraction element. The pin retraction element allows manual withdrawal of the frangible pins in the event that the lower deck section vertically deflects but the frangible pins do not shear. The frangible pins are located only on the flight deck (aircraft flight crew) side of the door assembly to prevent access from the passenger side of the door assembly. In another aspect of the invention, a handle is also provided on the door assembly flight deck side to aid in lower door section manual removal.
In one preferred embodiment of the invention, an aircraft door is provided comprising a door upper section having a lower engagement edge, and a door lower section having an upper engagement edge. The lower engagement edge of the door upper section slidably couples with the upper engagement edge of the door lower section to form a sliding joint. The sliding joint is disposed between the two door sections at an angle measured from a horizontal plane passing through the sliding joint. The door upper section is joined to the door lower section by the sliding joint and together form a door assembly.
In another preferred embodiment of the present invention, a method to join sections of an aircraft flight deck door is provided. The method comprises the steps of forming an upper door section having a hinged side edge and a lower edge; fastening the lower edge of the upper door section to the upper member of a two member sliding mechanical joint; slidably joining the upper member of the sliding joint to a lower member of the sliding joint with a combination of an extension element of each member received by a corresponding receiving slot of each member; fastening the lower member of the sliding mechanical joint to an upper edge of the lower door section; disposing the sliding joint between the door sections at an angle measured from a horizontal plane passing through the sliding joint; and rotatably supporting the door about the hinged side of said upper door edge.
In still another preferred embodiment of the present invention, the attached pin retraction element of the frangible pins is provided as a lever and cam assembly. The lever and cam assembly provides additional force to lift the frangible pin(s) out when the vertical load of the deck displacement jams the lower door section but does not shear the frangible pin(s). The lever and cam assembly also provides the force necessary to completely shear a partially sheared frangible pin.